Carpet is typically made of synthetic polymeric fibers which are sewn into a backing layer. The backing layer is typically disposed on a foam pad which rests on a flooring surface and the fibers extend upwardly therefrom.
Carpet and other fabric fibers may be soiled in a variety of ways. With carpet, the daily act of walking from outside conditions onto carpet is a common way that soiling may occur. Another soiling condition is caused by the spilling of food, beverages and other contaminates on carpet or other fabric fibers. Further, continuous contact between damp fibers and objects containing iron may also cause rust stains to be deposited.
A less known cause of fabric soiling occurs by the cleaning of carpet and other fibers using some water based cleaners. These cleaners may remove protectants initially applied to the carpet fibers as well as deposit a substantial amount of inorganic salts such as iron, calcium and magnesium salts. Many of these salts involve iron (II) as the cationic member. Because most common carpet cleaners known in the art are water based, the act of cleaning will cause carpet or other fibers to be dampened by those water based cleaners. Although the carpet is dried following the cleaning, some water will inevitably remain on the carpet. Therefore, because the water used for cleaning contains inorganic salts, e.g., iron salts, the very act of cleaning the carpet with a water based cleaner will often deposit these inorganic salts on the carpet fibers. Although thorough rinsing may minimize the iron salt deposition on carpet or other fibers, because rinse water contains iron salts, it will also deposit these undesirable salts onto the fibers.
Iron salts are not per se damaging to the carpet. However, iron salts have the propensity to form carpet discoloration. The discolorations are often the result of the oxidation of these iron salt to an iron oxide species. Most iron oxide species are red or rust colored. As such, the deposit of iron oxide salts on the fibers of the carpet may cause a rust colored stain. Unfortunately, iron oxide salts are water insoluble, thereby precluding their removal through simple, ordinary, washing. Additionally, inorganic salts other than iron oxides can also cause stains on carpet. For example, magnesium and calcium hydroxides are likewise water insoluble and may cause an undesirable discoloration of the carpet.
Carpet cleaners known in the art rely on either surfactants or an effervescing action to lift and remove oil and dirt from the carpet. However, because inorganic salts such as iron oxides are insoluble in water, these cleaners are unable to remove such stains. Moreover, inorganic salts tend to adhere to the carpet fibers and/or become intertwined in the fibers. Through either interaction, the salt particles are not easily washed out of the carpet through conventional means.
Additionally, there are numerous ways in which a carpet becomes soiled and discolored. If the discoloration is caused by insoluble inorganic salts, the cleaning methods known in the art cannot effectively remove the stains. In addition to the oxidation of iron salts, it is not uncommon for a person to contact an item covered with iron oxide (rust) with the person's shoes, etc. The iron oxide is then carried onto the carpet where is often leaves a very noticeable discoloration.
Unfortunately, as indicated above, iron oxide is relatively difficult to remove from carpet and other textiles due in part to its insolubility in water. Thus, for years rust stains on carpet and other fibers were treated with hydrofluoric acid (HF). Hydrofluoric acid, however, is extremely dangerous, in that it can readily burn the skin and has been documented to penetrate the skin and degrade underlying bone. Thus, while hydrofluoric acid was an effective method of removing rust stains, the risks associated with the compound required cleaning companies to find a safer alternative. Thus, most cleaning solutions targeted at the removal of rust use ammonium bifluoride. Like hydrofluoric acid, ammonium bifluoride improves the solubility of rust. Additionally, ammonium bifluoride is safer to use than hydrofluoric acid, but may not be as effective as the more hazardous hydrofluoric acid cleaners.
Therefore, it would be useful to provide a carpet stain removal process that would enable the removal of normally insoluble rust stains, and yet, be as effective as the use of hydrofluoric acid while maintaining a good safety level for those using the process. The salvation of these rust stains in an aqueous environment would allow the stains to be removed from the carpet fibers, regardless of how they were retained by the fibers.